Brushless motor, and disk drive equipped with the same

ABSTRACT

In a brushless motor for use in a disk drive, a rotor is mounted onto a tube portion of a housing. A retaining claw is formed at an upper end of the tube portion. A turntable has a central concave portion which accommodates an upper portion of the tube portion of the housing. A retaining member is provided radially outside the central concave portion, and includes a plurality of retaining pieces extending to the inside of the central concave portion. When the rotor is mounted onto the housing, the retaining pieces come into contact with the retaining claw and then move upward. When the rotor moves upward relative to the housing, the retaining pieces come into contact with the retaining claw, thereby restricting upward movement of the rotor. Upward movement of the retaining pieces is restricted by contact between the retaining member and the turntable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/866,721, filed on Oct. 3, 2007 which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2006-272128, filed on Oct. 3, 2006, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a brushless motor to be equipped in adisk drive for recording and reproducing or for simply reproducinginformation stored on an optical disk. In particular, the presentinvention relates to improvement in a rotor retaining mechanism inaccordance with a thinned brushless motor.

2. Description of the Related Art

A personal computer mainly used as a portable device has been developedto become lighter and thinner for better portability. Accordingly, it isrequired to thin a disk drive to be equipped in the personal computer.Reduction in thickness can be achieved by adopting a slot-in disk drivefor directly dragging a plate-shaped disk thereinto since this type ofdisk drive requires no tray for mounting a disk. Such improvement is notsufficient and there is still a demand for a further thinned personalcomputer. In order to fulfill such a demand, it is required to furtherthin a spindle motor (brushless motor) to be equipped in a disk drive,as well as to thin the disk drive itself to be equipped in the personalcomputer.

Improvement in a rotor retaining mechanism is one of objects to beachieved for obtaining a thinner brushless motor. There are, forexample, two types of rotor retaining mechanisms such as a shaftretaining type and a hook-shaped type.

An entire structure of the brushless motor is described with referenceto FIGS. 7 and 8. FIGS. 7 and 8 are schematic views respectively showingthese two types of retaining mechanisms. Each of FIGS. 7 and 8 is apartial cross-sectional view of the brushless motor to be equipped in adisk drive. In these drawings, like parts are given like referencenumerals.

The brushless motor includes a rotor 100 for allowing a disk-shapedstorage medium (hereinafter, simply referred to as a storage disk) suchas a CD (compact disc) to be removably mounted thereon, a bearing 101for supporting the rotor 100 in a rotatable manner, a housing 102, andthe like. The rotor 100 has a turntable 103 in a substantially diskshape for allowing a storage disk to be mounted on an upper surfacethereof, a chucking device 104 incorporated in the upper surface of theturntable 103 and allowing the storage disk to be removable, a shaft 105and a rotor magnet 106 respectively attached integrally to the turntable103. The bearing 101 for supporting the shaft 105 in a rotatable manneris fixed in the housing 102 to be mounted to a mounting plate 107. On anopposite side of the housing 102 to the shaft 105, there is fixed astator 108 facing the rotor magnet 106 with a space therebetween andgenerating a rotational magnetic field to rotary drive the rotor 100. Apressurizing magnet 109 is arranged between the turntable 103 and thehousing 102. The turntable 103 can be stably rotated since the turntable103 is attracted toward the housing 102 by magnetic force.

The rotor 100 is mounted onto the housing 102 and the like by, forexample, inserting the shaft 105 into the bearing 101. The rotorretaining mechanism is provided for preventing the mounted rotor 100from dropping off the bearing 101.

As shown in FIG. 7, an example of the rotor retaining mechanism of theshaft retaining type includes a groove 110 formed near a lower end ofthe shaft 105 of the rotor 100 over the entire circumferential length ofthe shaft 105, and a retaining member 113 fixed to the housing 102 withone end 111 thereof placed inside the groove 110. According to such aconfiguration, the end 111 of the retaining member 113 butts an innerbottom surface 114 of the groove 110 before the rotor 100 completelydrops off due to upward movement of the shaft 105, thereby preventingthe rotor 100 from dropping off.

FIG. 8 shows an example of the rotor retaining mechanism of thehook-shaped type. This rotor retaining mechanism includes a retainingmember 121 attached onto a bottom surface of the turntable 103 of therotor 100 with an elastic spring arm 120 having an end in a hook shapein cross section and projecting toward the housing 102, and an engagingportion 122 provided at one end of a tube portion of the housing 102 andengaged with the hook-shaped end of the retaining member 121. Accordingto such a configuration, the spring arm 120 is elastically deformed ifthe hook-shaped end of the retaining member 121 and the engaging portion122 come into contact with each other while the rotor 100 is mountedonto the housing 102 and the like. Moreover, if force which forces therotor 100 to drop off is applied to the rotor 100 after the rotor 100has been mounted onto the housing 102 and the like, the rotor 100 isprevented from dropping off since the hook-shaped end of the retainingmember 121 and the engaging portion 122 butt with each other.

SUMMARY OF THE INVENTION

A brushless motor according to the present invention includes a rotorand a housing. The rotor has a turntable for allowing a disk with amounting hole formed at a center thereof to be mounted thereonto, and ashaft mounted directly or indirectly to the turntable to serve as arotational axis. The housing has a bearing for rotatably supporting theshaft, and a tube portion with an inner peripheral surface for fixingthe bearing.

The turntable has a central concave portion in a concave shape openeddownwards in an axial direction. The central concave portion partiallyhouses the tube portion of the housing. On an upper and outer surface ofthe tube portion of the housing, there is formed a retaining clawprojecting radially outwards.

A retaining member is attached onto a bottom surface of the turntable.The retaining member includes a mounting base and a plurality ofretaining pieces. In a state where the rotor is mounted onto thehousing, the retaining member is arranged axially below the retainingclaw.

When mounting the rotor onto the housing, due to contact between theplurality of retaining pieces and the retaining claw, outer peripheralportions of the retaining pieces are inclined axially downwards andinner peripheral portions of the retaining pieces in contact with theretaining claw are inclined axially upwards.

When the rotor moves axially upwards with respect to the housing afterthe rotor has been mounted onto the housing, the inner peripheralportions contact the retaining claw and the outer peripheral portionscontact the bottom surface of the turntable.

Other features, elements, advantages and characteristics of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a brushless motor according to a preferredembodiment of the present invention seen from above.

FIG. 2 is a cross-sectional view of the brushless motor of FIG. 1, cutalong line A-A in FIG. 1.

FIG. 3A is a plan view of a retaining member of the brushless motor ofFIG. 1 seen from above, and FIG. 3B is a cross-sectional view of theretaining member of FIG. 3A cut along line B-B in FIG. 3A.

FIG. 4 illustrates a shape change of a retaining member when a rotor ismounted onto a housing in the brushless motor of FIG. 1.

FIG. 5 illustrates a shape change of the retaining member when force forseparating the rotor from the housing is applied to the rotor.

FIG. 6 is a cross-sectional view of a disk drive equipped with thebrushless motor of FIG. 1 according to a preferred embodiment thepresent invention, cut along a rotational axis of the brushless motor.

FIG. 7 is a cross-sectional view of an exemplary conventional retainingmechanism for the brushless motor.

FIG. 8 is a cross-sectional view of another exemplary conventionalretaining mechanism for the brushless motor.

FIG. 9 shows a brushless motor according to another preferred embodimentof the present invention.

FIG. 10 shows a shape change of a retaining member of the brushlessmotor of FIG. 9 when a rotor is mounted onto a housing in the brushlessmotor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 6, 9 and 10, preferred embodiments of thepresent invention will be described in detail. It should be noted thatin the explanation of the present invention, when positionalrelationships among and orientations of the different components aredescribed as being up/down or left/right, ultimately positionalrelationships and orientations that are in the drawings are indicated;positional relationships among and orientations of the components oncehaving been assembled into an actual device are not indicated.Meanwhile, in the following description, an axial direction indicates adirection parallel to a rotation axis, and a radial direction indicatesa direction perpendicular to the rotation axis.

FIG. 1 is a plan view of a brushless motor according to a preferredembodiment of the present invention, seen from above. FIG. 2 is across-sectional view of the brushless motor of FIG. 1, cut along lineA-A in FIG. 1. The brushless motor has such a dimension that a turntable6 shown in FIG. 1 has a diameter of approximately 3 cm.

The brushless motor includes a rotor R for rotating an optical storagemedium disk in the form of a disk mounted thereonto about a rotationalaxis, a bearing 1 for supporting the rotor R in a rotatable manner, ahousing 2, a stator 3, a pressurizing magnet 4, a retaining member 5,and the like. Examples of the optical storage medium are CD and DVD.

The rotor R includes the turntable 6 in a substantially disk shape, achucking device 7 attached on a central portion of the turntable 6, ashaft 8 attached at a center of the turntable 6 along an axial directionsubstantially parallel to the rotational axis, and a rotor magnet 10attached at an outer peripheral portion of the turntable 6.

The turntable 6 is formed by pressing a thin magnetic steel plate madeof stainless steel, for example. Referring to FIG. 2, the turntable 6includes a lid portion 11 and a cylindrical portion 12. The lid portion11 has a substantially circular disk shape. An outer peripheral portionof the lid portion 11 is slightly raised. The turntable 6 also includesa cylindrical portion 12 extending downwards from an outer peripheraledge of the lid portion 11. At a center of the lid portion 11, a centralconcave portion 14 and a shaft fixing portion 15 are formed. The centralconcave portion 14 is hollow and cylindrical about the rotation axis Jand extends upward from the lid portion 11. The shaft fixing portion 15extends axially upward from the central concave portion 14 and is hollowand cylindrical about the rotation axis J. A diameter of the shaftfixing portion 15 is smaller than that of the central concave portion14. There is formed an opening penetrating from an upper surface to alower surface of the turntable 6 at an upper end of the shaft fixingportion 15. Axial centers of the turntable 6, the central concaveportion 14, and the shaft fixing portion 15 are identical to an axialcenter J serving as the rotational axis.

Attached to an outer peripheral edge of the upper surface of theturntable 6 is a disk supporting member 16 made of rubber or the like,for receiving and supporting an optical disk. The rotor magnet 10 madeof a permanent magnet is fixed onto an inner peripheral surface of thecylindrical portion 12 of the turntable 6. Structural strength of theturntable 6 is increased by provision of a plurality of bent portionssuch as the central concave portion 14 and the shaft fixing portion 15at the center of the lid portion 11 by press work. Thus, the turntable 6may be made of an ultrathin steel plate (having a thickness ofapproximately 0.3 mm in the present embodiment). Radially outside thecentral concave portion 14, there is formed a flat surface portionextending radially outwards. An inner peripheral surface of the centralconcave portion 14 and a lower surface of the flat surface portion areconnected to each other with a curved surface.

With reference to FIG. 1, the chucking device 7 includes a centeringcase 18 in a generally cylindrical shape, center adjusting claws 19formed integrally with the centering case 18, dog members 20 for holdingan optical disk, and the like. In the present preferred embodiment,three center adjusting claws 19 and three dog members are equiangularlyarranged along an outer periphery of the centering case 18. The dogmembers 20 are constantly biased radially outwards by coil springs 22provided in the centering case 18. An optical disk with a mounting holeformed at a center thereof is removably mounted onto the turntable 6 byfitting the mounting hole to the centering case 18 from upwards.

The shaft 8 is made of material which is excellent in abrasionresistance, e.g., stainless steel. The shaft 8 is inserted into theshaft fixing portion 15 of the turntable 6 and is fixed integrallytherewith such that a lower end of the shaft 8 projects downwards. Theshaft 8 is fixed coaxially with the axial center J of the turntable 6and the chucking device 7. While the turntable 6 and the shaft 8 areseparately formed from each other in the present preferred embodiment,the turntable 6 and the shaft 8 may be integrally formed. Moreover, theshaft 8 may be fixed indirectly to the turntable 6 with another memberinterposed therebetween, instead of being fixed directly to theturntable 6.

The bearing 1, the housing 2, the stator 3, the pressurizing magnet 4,the retaining member 5, and the like are respectively arranged under thelid portion 11 of the turntable 6 of the rotor R.

The housing 2 has a tube portion 23 in a generally cylindrical shape,and a fixing base portion 24 extending radially outwards from an axiallylower portion of the tube portion 23. An inward projection 25 and anoutward projection 27 are provided on a bottom surface of the fixingbase portion 24. The inward projection 25 is provided radially insidethe outward projection 27. Formed at an outer periphery of an uppersurface of the fixing base portion 24 is an outward step 28 having aperipheral surface along the axial direction and a flat surfaceextending radially outwards from a lower end of the peripheral surface.The stator 3 is fixed onto the outward step 28. On the other hand, aninward step 29 is formed radially inside the outward step 28, the inwardstep 29 having a peripheral surface along the axial direction and a flatsurface extending radially inwards from a lower end of the peripheralsurface. The pressurizing magnet 4 is fixed onto the inward step 29.

The tube portion 23 has an inner surface defining a through hole 30penetrating through the housing 2 in the axial direction. The bearing 1is fixed onto the inner peripheral surface of the tube portion 23. Aretaining claw 31 projecting radially outwards is formed on an upper andouter peripheral surface of the tube portion 23. The retaining claw 31is formed integrally with the tube portion 23. The retaining claw 31 hasan inclined surface 33 inclined with respect to the axial direction suchthat it moves away from the axis J as it moves downwards. The retainingclaw 31 further includes a flat surface 34 which is substantiallyperpendicular to the axial direction and extends from a lower end of theinclined surface 33 radially inwards (refer to FIGS. 4 and 5). At leastthe upper end of the tube portion 23 formed with the retaining claw 31is housed within the central concave portion 14 of the turntable 6.

A lower side of the opening in the tube portion 23 of the housing 2 iscovered with a bottom lid 35. The bottom lid 35 is fixed by beingsandwiched between the bottom surface of the fixing base portion 24 andthe inward projection 25 of the housing 2. In other words, the bottomlid 35 is fixed to the housing 2 by crimping. On an upper surface of thebottom lid 35, there is arranged a thrust plate 36 having a generallydisk shape and receiving the lower end surface of the shaft 8. Amounting plate 38 is fixed to an outer periphery of the bottom surfaceof the fixing base portion 24. The mounting plate 38 is fixed by beingsandwiched between the bottom surface of the fixing base portion 24 andthe outward projection 27. In other words, the mounting plate 38 isfixed to the housing 2 by crimping. The mounting plate 38 covers a lowerside of the turntable 6.

The stator 3 includes a stator core 40 having a core back portion in agenerally annular shape and a plurality of teeth respectively extendingradially outwards from the core back portion and circumferentiallyspaced apart from one another, and coils 43 formed by winding conductivewires around each of the teeth of the stator core 40. The stator 3radially faces the rotor magnet 10 attached to the turntable 6 with aspace therebetween. The rotor magnet 10 is rotated integrally with theturntable 6 and the shaft 8 due to a rotational magnetic field generatedby the stator 3.

The pressurizing magnet 4 is made of a permanent magnet in an annularshape. The pressurizing magnet 4 magnetically attracts the turntable 6toward the housing 2, and stabilizes rotation of the rotor R. Thepressurizing magnet 4 is arranged so as to axially face the lid portion11 of the turntable 6. The pressurizing magnet 4 is arrangedsubstantially coaxially with the axial center J of the rotor R, and isfixed onto the inward step 29 of the fixing base portion 24. Further,the pressurizing magnet 4 is arranged such that an inner peripheralsurface thereof is radially spaced apart from the outer peripheralsurface of the tube portion 23. In such a configuration, an adequatespace in the axial direction can be provided under the turntable 6.Therefore, the brushless motor can be thinned even when a pressurizingmagnet 4 having a large volume is used.

The retaining member 5 is obtained by pressing a thin metal plate. Aspecific structure of the retaining member 5 is shown in FIGS. 3A and3B. FIG. 3A is a plan view of the retaining member 5. FIG. 3B is across-sectional view of the retaining member 5 of FIG. 3A, cut alongline B-B and seen in a direction of an arrow in FIG. 3A. As shown inFIG. 3A, the retaining member 5 is formed into a generally annularshape. The retaining member 5 includes a plurality of mounting bases 44(five in the present embodiment) arranged to be circumferentially spacedapart from one another, a plurality of retaining pieces 45 (five in thepresent embodiment) each arranged between the circumferentially adjacentmounting bases 44, and a plurality of pairs of supporting portions 46,46 for connecting the respective mounting bases 44 and the respectiveretaining pieces 45. All the mounting bases 44, the retaining pieces 45,and the supporting portions 46 are integrally formed by press work.

Each of the mounting bases 44 has a generally circular arc shape. Asshown in FIG. 3B, each of the mounting bases 44 is formed with aplurality of projections 48 (in the present embodiment, two for each ofthe mounting bases 44) along a circumferential direction, and theprojections 48 are to be welded when the mounting bases 44 are fixed tothe turntable 6. The plurality of projections 48 are formed by concavingthe mounting bases 44.

Each of the retaining pieces 45 is formed into a generally rectangularshape radially elongated with rounded corners. Each of the retainingpieces 45 is supported with respect to the circumferentially adjacentmounting bases 44 by the pair of supporting portions 46, 46 each havinga thin bar shape and circumferentially projecting from bothcircumferential side surfaces of each of the retaining pieces 45. Eachof the retaining pieces 45 has an inner peripheral portion 49 extendingradially inwards from the supporting portions 46, and an outerperipheral portion 50 (outwardly extending portion) extending radiallyoutwards from the supporting portions 46. Each of the inner peripheralportions 49 projects radially inwards from the inner peripheral edges ofthe mounting bases 44.

The supporting portions 46 have a radial width smaller than that of themounting bases 44. Each of the supporting portions 46 is formed radiallyinside a center of the radial width of each of the mounting bases 44.Since the radial width of the supporting portions 46 is made smallerthan the radial width of the mounting bases 44, in a case where force isapplied to the inner peripheral portion 49 or the outer peripheralportion 50 of each of the retaining pieces 45 and around the adjacentsupporting portions, the supporting portions 46 bow and the retainingpiece 45 can rotate with the adjacent supporting portions 46 serving assupporting points. Moreover, since each of the supporting portions 46 isformed radially inside the center of the radial width of the mountingbases 44, the inner peripheral portions 49 of the retaining pieces 45are easily moved axially upwards and are not easily moved axiallydownwards.

As shown in FIG. 2, the retaining member 5 is attached onto the bottomsurface of the turntable 6. Specifically, the retaining member 5 isfixed to the peripheral edge of the central concave portion 14 so thatthe mounting bases 44 are located radially outside the central concaveportion 14. In a state where the retaining member 5 is fixed to theturntable 6, at least distal ends of the inner peripheral portions 49 ofthe retaining pieces 45 project radially inside the central concaveportion 14. When the rotor R is mounted onto the housing 2, the innerperipheral portions 49 of the retaining pieces 45 come into contact withthe retaining claw 31 (refer to FIGS. 4 and 5). After the rotor R hasbeen mounted onto the housing 2, the retaining member 5 axially facesthe pressurizing magnet 4 fixed onto the housing 2 with a spacetherebetween. Further, the supporting portions 46 are located at thesame radial position as the inner peripheral edge of the flat surfaceportion of the turntable 6.

The retaining member 5 is preferably attached to the turntable 6 byresistance welding such as spot welding. Specifically, in a state wherethe distal ends of the projections 48 on the mounting bases 44 arebrought into contact with the turntable 6, the contact portions areheated by flowing electricity. The projections 48 and the turntable 6are fixed to each other by melting the contact portions therebetween andthen pressurizing. By providing the projections 48 to be welded,portions to be welded can be clearly defined and areas to be welded canbe decreased. Accordingly, it is possible to prevent deformation of theturntable 6 due to heat generated by welding. As a result, it ispossible to provide a brushless motor allowing a disk to be accuratelymounted.

With reference to FIGS. 4 and 5, described below is a retainingmechanism utilizing the retaining member 5 according to the presentpreferred embodiment of the present invention. The retaining mechanismincludes the retaining member 5, and the retaining claw 31 formed on thehousing 2.

The rotor R is mounted onto the housing 2 by combining the turntable 6,the chucking device 7, the rotor magnet 10, the retaining member 5, andthe like, and then inserting the shaft 8 of the rotor R into the bearing1 of the housing 2 combined with the pressurizing magnet 4, the stator3, and the like. FIG. 4 shows a relation between the retaining member 5and the retaining claw 31 when the rotor R is mounted onto the housing2.

With reference to FIG. 4, when the shaft 8 is inserted into the bearing1, the inner peripheral portions 49 of the retaining pieces 45 come intocontact with the inclined surface 33 of the retaining claw 31 (as shownby dashed-two dotted line in FIG. 4). Thus, force in an axially upwarddirection is gradually applied to the inner peripheral portions 49 ofthe retaining pieces 45 due to contact with the inclined surface 33.Because of such force, the inner peripheral edges of the innerperipheral portions 49 of the retaining pieces 45 move upwards while theinner peripheral portions 49 are elastically deformed upwards with thesupporting portions 46 serving as the supporting points. Further, sincethe supporting portions 46 themselves bow, the inner peripheral portions49 are moved upwards and the outer peripheral portions 50 are moveddownwards with the supporting portions 46 serving as the supportingpoints. That is, the retaining pieces 45 are inclined such that it movesdownward as it moves radially outwards. It is possible to reduce forceto mount the rotor R onto the housing 2 due to contact between theinclined surface 33 and the retaining pieces 45. In addition, the forceto mount the rotor R onto the housing 2 can be further reduced due toelastic deformation of the inner peripheral portions 49. As a result, itis possible to prevent deformation of the turntable 6 by the force tomount the rotor R onto the housing 2, even when the turntable 6 is madethinner in accordance with the thinned brushless motor.

The supporting portions 46 in the retaining member 5 are preferablyarranged at the inner peripheral edge of the flat surface portion of theturntable 6. Since the curved surface is formed to connect the innerperipheral edge of the flat surface portion and the inner peripheralsurface the central concave portion 14, it is possible to reduce forceapplied from the turntable 6 onto the upper surfaces of the innerperipheral portions 49 when the inner peripheral portions 49 areelastically deformed. Further, since the inner peripheral portions 49 donot contact the bottom surface of the turntable 6, the retaining pieces45 easily bow in the vicinity of the supporting portions 46.Consequently, it is possible to reduce the force to mount the rotor Ronto the housing 2.

It is preferable that the inclined surface 33 be formed so as to allowthe inner peripheral portions 49 to be elastically deformed and returnto its original state at least reversibly when the inner peripheralportions 49 of the retaining pieces 45 move axially upwards. Thesupporting portions 46 are arranged at the inner peripheral edge of theflat surface portion of the turntable 6, thereby reducing a radius ofaxially upward movement of the inner peripheral portions 49 with thesupporting portions 46 serving as the supporting points. Thus, bowing ofthe inner peripheral portions 49 is made smaller and the supportingportions 46 are easily made to bow. As a result, plastic deformation ofthe inner peripheral portions 49 can be prevented.

In order to obtain a thinner brushless motor, it is also desirable tominimize the space between the retaining member 5 and the pressurizingmagnet 4 that axially face with each other. However, in the presentembodiment, the distance between the retaining member 5 and thepressurizing magnet 4 is made larger than an axial distance of axiallydownward movement of the outer peripheral portions 50 of the retainingpieces 45. Accordingly, it is possible to reduce the force to mount therotor R onto the housing 2. Further, extreme plastic deformation of ordamage to the supporting portions 46 may occur due to excessive movementof the retaining pieces 45 when mounting the rotor R onto the housing 2.According to the present embodiment, such excessive movement can beprevented due to contact between the outer peripheral portions 50 of theretaining pieces 45 and the upper surface of the pressurizing magnet 4.

FIG. 5 shows a relation between the retaining member 5 and the retainingclaw 31 when force to drop off the rotor R with respect to the housing 2(an axially upward direction in FIG. 5) is applied to the rotor R. Asshown in FIG. 5, when the force to drop off the rotor R with respect tothe housing 2 is applied to the rotor R and the rotor R moves axiallyupwards with respect to the housing 2, the inner peripheral portions 49of the retaining pieces 45 are brought into contact with the verticalsurface 34 of the retaining claw 31 (as shown by dashed-two dotted linein FIG. 5). Further, when the force to drop off the rotor R with respectto the housing 2 is applied to the rotor R, the inner peripheralportions 49 of the retaining pieces 45 are elastically deformeddownwards. In such a state, even when the supporting portions 46 bow sothat the inner peripheral portions 49 of the retaining pieces 45 aredownwardly moved, such downward movement of the inner peripheralportions 49 is restricted due to contact between the outer peripheralportions 50 and the bottom surface of the turntable 6. In other words,the retaining pieces 45 themselves hardly move downwards. Accordingly,the retaining pieces 45 cannot move to an upper side of the retainingclaw 31 unless the inner peripheral edges of the inner peripheralportions 49 are deformed so as to be located radially outside the outerperipheral edge of the retaining claw 31. In particular, since thesupporting portions 46 are formed at the inner peripheral edge of theflat surface portion of the turntable 6, the radial distance between thesupporting portions 46 and the retaining claw 31 can be reduced, therebymaking deformation of the inner peripheral portions 49 more difficult.As a result, the rotor R can be securely prevented from dropping offwith respect to the housing 2.

It is desirable that the radial width of the outer peripheral portions50 of the retaining pieces 45 be larger than the radial width of theinner peripheral portions 49. According to such a structure, even whenthe force to drop off the rotor R with respect to the housing 2 isapplied to the rotor R, the retaining pieces 45 can be more securelysupported since the areas of contact between the bottom surface of theturntable 6 and the outer peripheral portions 50 can be increased.

A brushless motor according to another preferred embodiment of thepresent invention is now described referring to FIGS. 9 and 10. In thefollowing description, a retaining member thereof is mainly described.FIG. 9 is a cross-sectional view of the brushless motor of thispreferred embodiment of the present invention, taken along its axialdirection. FIG. 10 shows the shape change of the retaining member 5 awhen the rotor R is mounted to the housing 2. The brushless motor ofthis preferred embodiment is similar to that of the above preferredembodiment and differences between them are mainly described in thefollowing description. Like components are given like reference numeralsand the detailed description thereof is omitted.

Referring to FIG. 9, the retaining piece 45 a of the retaining member 5a is bent upward at a point below the inner circumferential surface ofthe central concave portion 14, so that a portion 45 a 1 of theretaining piece 45 a located radially inside that point is at an angleto the axial and radial directions. This portion 45 a 1 is referred toan inclined portion 45 a 1. Except for the inclined portion 45 a 1, theretaining member 5 a is the same as the retaining member of the abovepreferred embodiment. A radially inner end of the inclined portion 45 a1 is located radially inside the radially outer end of the retainingclaw 31 of the housing 2.

Referring to FIG. 10, the shape change of the retaining member 5 a isnow described. When the rotor R is mounted to the housing 2, a lowersurface of the inclined portion 45 a 1 comes into contact with theinclined surface 33 of the retaining claw 31 and thereafter the inclinedportion 45 a 1 moves axially upward. An angle θ1 formed by the lowersurface of the inclined portion 45 a 1 located at the axially uppermostposition and the rotation shaft J1 is equal to or smaller than an angleθ2 formed by the inclined surface 33 and the rotation shaft J1. Withthis configuration, it is possible to prevent the inclined portion 45 a1 from applying large force to the inclined surface 33 when the rotor Ris mounted onto the housing 2. Therefore, force required for mountingthe rotor R onto the housing 2 can be reduced.

<Disk Drive>

With reference to FIG. 6, there is described a disk drive equipped withthe brushless motor of the preferred embodiment of the presentinvention. FIG. 6 is a cross-sectional view of the disk drive.

With reference to FIG. 6, the disk drive includes a brushless motor 200for allowing a disk D to be removable and rotating the disk D, anoptical pickup 201 for radiating light onto the disk D and emitting thelight reflected from the disk D, a moving mechanism 202 forreciprocating the optical pickup 201 along a radial direction of thedisk D, and a housing 203 for housing the brushless motor 200, theoptical pickup 201, and the moving mechanism 202.

The moving mechanism 202 includes a motor 204, and a gear 205 forreceiving rotary torque transmitted from the motor 204.

In the housing 203, a partition 206 is arranged for separating the diskD from the moving mechanism 202. The housing 203 is formed with anopening 207 for allowing the disk D to be inserted and taken outtherethrough.

The optical pickup 201 includes a light emitting and receiving portion208 for emitting and receiving a laser beam, and a moving portion 209 tobe engaged with the gear 205. The moving portion 209 is radiallyreciprocated along with the gear 205 to be rotary driven by the motor204. The light emitting and receiving portion 208 is radiallyreciprocated along with reciprocation of the moving portion 209.

By mounting the brushless motor according to the above preferredembodiment of the present invention, the disk drive can be easilythinned.

While there have been described the brushless motor and the disk driveaccording to the above preferred embodiment of the present invention,the present invention is not limited thereto, but various modificationscan be made within the scope of the appended claims.

For example, while the retaining member 5 according to the abovepreferred embodiment of the present invention has the annular shape, thepresent invention is not limited thereto, but the retaining member 5 mayhave a substantially circular arc shape like a partially missing circle.Further, while five retaining members 5 are formed in the abovepreferred embodiment, three retaining members 5 may be alternativelyformed. When three or five retaining pieces 45 are formed, the retainingmember 5 is well balanced and the circumferential width of the mountingbases 44 can be adequately secured. Therefore, the retaining member 5and the turntable 6 are easily welded. As a result, it is possible toimprove productivity of the brushless motor.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A brushless motor comprising: a rotor rotatable about a rotation axisand including a shaft centered on the rotation axis; a turntable in agenerally disk shape mounted directly or indirectly to the shaft andallowing a disk with a mounting hole formed at its center to be mountedthereonto; and a rotor magnet rotating integrally with the turntable andthe shaft; a bearing supporting the shaft in a rotatable manner; ahousing having a tube portion with an inner peripheral surface ontowhich the bearing is fixed; and a stator facing the rotor magnet with aspace therebetween and generating a rotational magnetic field, whereinthe housing has, on an upper and outer surface of the tube portion, aretaining claw projecting radially outwards, the turntable has a centralconcave portion in a concave shape opened axially downwards, the centralconcave portion housing at least an upper end of the tube portion, theturntable is attached with a retaining member radially outside thecentral concave portion, the retaining member includes: a mounting baseattached to the turntable; and a plurality of retaining pieces havinginner peripheral portions extending axially below the retaining claw ina state where the rotor is mounted onto the housing, when the rotor ismounted onto the housing, due to contact between the plurality ofretaining pieces and the retaining claw, the inner peripheral portionsof the plurality of retaining pieces in contact with the retaining claware inclined axially upwards, and when the rotor moves axially upwardswith respect to the housing, the inner peripheral portions contact theretaining claw.
 2. The brushless motor according to claim 1, wherein theretaining claw has: an inclined surface inclined axially downwardstoward a radially outer side, the inclined surface contacting theretaining pieces when mounting the rotor onto the housing; and avertical surface substantially vertical to the rotational axis, thevertical surface contacting the retaining pieces when the rotor movesaxially upwards with respect to the housing.
 3. The brushless motoraccording to claim 1, wherein the retaining member is made of a platemember having one of a substantially circular arc shape and asubstantially annular shape, the mounting base has a circular arc shape,and a plurality of mounting bases are arranged to be circumferentiallyspaced apart from one another, each of the retaining pieces is providedbetween the circumferentially adjacent mounting bases, and the mountingbases and the retaining pieces are respectively connected via supportingportions having a radial width smaller than a radial width of themounting bases.
 4. The brushless motor according to claim 3, whereineach of the supporting portions is formed radially inside a center ofthe radial width of the mounting bases.
 5. The brushless motor accordingto claim 3, wherein each of the retaining pieces has an outwardlyextending portion extending radially outwards from the supportingportions.
 6. The brushless motor according to claim 5, wherein theoutwardly extending portion has a radial width larger than a radialwidth of each of the retaining pieces between the supporting portionsand a radially inner end.
 7. The brushless motor according to claim 3,wherein when mounting the rotor onto the housing, a portion of each ofthe retaining pieces radially inside the supporting portions movesaxially upwards.
 8. The brushless motor according to claim 7, whereinthe turntable has a flat surface portion extending radially outwardsfrom a lower end of the central concave portion, and the supportingportions are arranged at an inner peripheral edge of the flat surfaceportion.
 9. The brushless motor according to claim 8, wherein an innerperipheral surface of the central concave portion and a lower surface ofthe flat surface portion are connected with a curved surface.
 10. Thebrushless motor according to claim 1, wherein the retaining member isobtained by pressing metal, and at least the mounting base and theretaining piece are integrally formed by punching.
 11. The brushlessmotor according to claim 1, wherein the mounting base is formed with aplurality of projections circumferentially spaced apart from oneanother, and in a state where the plurality of projections are broughtinto contact with the turntable, the retaining member is fixed to theturntable by melting the plurality of projections.
 12. The brushlessmotor according to claim 11, wherein each of the retaining member andthe turntable is made of an electrical conducting material, and theplurality of projections are melted by flowing electricity between theplurality of projections and the turntable.
 13. The brushless motoraccording to claim 1, wherein at least a part of the turntable is madeof a magnetic material, the housing is arranged, on an upper surface,with a pressurizing magnet for attracting the turntable toward thehousing, the pressurizing magnet is arranged to have a portionsubstantially identical in radial position to the retaining member, andto face the retaining member with an axial distance therebetween, andthe distance between the retaining member and the pressurizing magnet islarger than an axial distance of axially downward movement of theretaining pieces when mounting the rotor onto the housing.
 14. Thebrushless motor according to claim 1, wherein three or five of theretaining pieces are equiangularly arranged.
 15. The brushless motoraccording to claim 1, wherein a portion of each of the retaining pieces,located radially inside an inner surface of the central concave portion,has a lower surface, a radially inner end of the lower surface beingabove any other portions of the lower surface and below the retainingclaw.
 16. The brushless motor according to claim 10, wherein a portionof each of the retaining pieces, located radially inside an innersurface of the central concave portion, has a lower surface, a radiallyinner end of the lower surface being above any other portions of thelower surface.
 17. The brushless motor according to claim 2, wherein theinner peripheral portion includes an inclined portion located radiallyinside an inner surface of the central concave portion, the inclinedportion being inclined with respect to the rotation axis such that aradially inner end of the lower surface is above any other portions ofthe lower surface, and an acute angle formed by the inclined portion ofeach of the retaining pieces when the retaining member is in contactwith the inclined surface of the retaining claw is equal to or smallerthan an acute angle formed by the inclined surface of the retaining clawand the rotation axis.
 18. A disk drive comprising: the brushless motoraccording to claim 15 rotating a disk; an optical pickup emitting lighttoward the disk and receiving the light reflected from the disk; and amoving mechanism radially moving the optical pickup.